Canopy structures such as installed at vehicle fuel dispensing service stations typically have flat roofs supported by hollow vertical columns made of corrodible material such as steel. Such columns are often used as conduits for draining water from the flat roof, thus exposing the interior of the columns to corrosive deterioration and loss of strength needed to support the roof. Since the deterioration of the columns may be entirely internal, they can weaken to a dangerous condition resulting in a collapse of the canopy without the owner or operating personnel being aware of their dangerously weakened condition.